3. Instruments of Microscopy:
1. Simple Microscopes:
Only have one lens, similar to a magnifying
glass.
Leeuwenhoeck’s simple microscopes allowed
him to magnify images from 100 to 300 X.
They were so difficult to focus, he built a new one for
each specimen, a total of 419.
He did not share his techniques with other scientists.
Even today, his source of lighting is unknown.
His daughter donated 100 of his microscopes to the
Royal Society shortly before his death in 1723.
4. Instruments of Microscopy:
2. Compound Light (CL) Microscopy
History of CL Microscopes:
First developed by Zaccharias Janssen, Dutch
spectacle maker in 1600.
Poor quality
Could not see bacteria
Joseph Jackson Lister (Lister’s father) developed
improved compound light microscope in 1830s.
Basis for modern microscopes
Use visible light as a source of illumination.
5. Instruments of Microscopy:
2. Compound Light Microscopy
Have several lenses:
1. Light originates from an illuminator and passes
through condenser lenses, which direct light onto the
specimen.
2. Light then enters the objective lenses, which magnify
the image. These are the closest lenses to the specimen:
Scanning objective lens: 4 X
Low power objective lens: 10 X
High power objective lens: 40-45 X
Oil immersion lens: 95-100 X
3. The image of the specimen is magnified once again by
the ocular lens or eyepiece (10 X).
6. Instruments of Microscopy:
3. Darkfield Microscopy
Useful to examine live or unstained specimens.
Light sensitive organisms
Specimens that lack contrast with their background.
Spirochetes which cause syphilis.
Darkfield condenser with opaque disc blocks
light that would enter objective lens directly:
Light reflects off specimen at an angle.
Only light reflected by specimen enters objective lens.
No direct background light.
Image: Light specimen against dark
background.
7. Instruments of Microscopy:
4. Phase Contrast Microscopy
Useful to examine live specimens:
Doesn’t require fixing or staining, which usually kill
and/or distort microorganisms.
Permits detailed examination of internal
structures.
Special objective lenses and condenser with ring
shaped diaphragm accentuate small differences in
refractive indexes of internal structures.
Image: Direct rays and reflected light rays come
together, forming an image with many shades of
gray to black.
8. Instruments of Microscopy:
5. Fluorescence Microscopy
Fluorescence: Ability of substances to absorb
short wavelengths of light (ultraviolet light) and
emit them at a longer wavelength.
Natural Fluorescence: Some microorganisms
fluoresce naturally under UV light (Pseudomonas).
Fluorochrome: Fluorescent dye.
Acridine orange: Binds to nucleic acids, colors cells orange,
green, or yellow depending on light source.
Immunofluorescence: Fluorescent antibodies can be
used to detect specific antigens. Very useful for the
rapid diagnosis of specific diseases (e.g.: syphilis).
Image: Luminescent bright object against a dark
background.
9. Instruments of Microscopy:
Limitations of light microscopy:
Magnification: Up to 2000 X.
Resolving Power: Up to 0.2 um.
Because of the limits of magnification and
resolving power, viruses and most internal
structures of cells cannot be seen with a light
microscope.
10. Instruments of Microscopy:
6. Electron Microscopy
Electron microscopes were first developed in
1932, and became widely available in 1940s.
Use a beam of electrons instead of a beam of
light.
Wavelength of electron beam is about 100,000 times
smaller than visible light.
Used to examine structures too small to be resolved
with a light microscope.
Two types of electron microscope:
A. Transmission Electron Microscope (TEM)
B. Scanning Electron Microscope (SEM)
11. 7. Scanning Tunneling Microscopy and
Atomic Force Microscopy (AFM)
Developed in the 1980s.
Used to observe structure and surface of
biological molecules and silicon computer chips.
A. Scanning Tunneling Microscope (STM)
Uses a thin metal probe that scans the surface of a
specimen.
B. Atomic Force Microscopy (AFM)
Uses a diamond and metal probe that scans
surface of specimen.
Advantages of both microscopes:
Higher resolving power than electron microscopes
No special specimen preparation required
